The present invention relates generally to open-end rotor spinning machines and more particularly to a spinning box for such machines.
When a yarn is broken at a spinning station of an open-end rotor spinning machine, or when spinning is to be started at a spinning station, a yarn end is inserted through the yarn withdrawal tube at the spinning station into the rotor in order to unite the yarn end with fibers delivered into the rotor from a sliver feed. The spinning process is initiated and progresses with the continuous feeding of fibers into the rotor and with the withdrawal of the yarn. The introduction of the yarn into the rotor as well as the delivery of the fibers must be precisely coordinated with one another in order that the area of the starter end of yarn does not differ in an unacceptable manner from the rest of the yarn in appearance and in quality.
A spinning start procedure requires particular care during the feeding in of the fibers. If a yarn breaks the sliver feed is immediately halted. The yarn is drawn as a rule out of the spinning chamber and therewith out of the rotor due to the high winding speed. It is customary to clean the rotor before every spinning start before the yarn is returned into the spinning chamber. This measure has a preventive nature in order to raise the quality of the yarn. Dirt which has collected in the rotor as well as fibers, which are problematic for the spinning start process, are to be removed by this cleaning. However, since the sliver remains introduced in the opening device, the opening cylinder continues to rotate and the spinning vacuum continues to be applied to the spinning chamber, it can not be excluded that fibers are transported into the rotor after a cleaning has been performed, while the standing rotor is waiting for the spinning start process, and collect at the lowest position in the fiber collection groove of the rotor. These uncontrolled fibers flying around in the spinning chamber can form flocks or stubs in the yarn by being deposited in the rotor during the spinning start and thus cause yarn defects. It is therefore important that no stray fibers settle in the rotor before the spinning start process. In order to be able to carry out the spinning start and the yarn formation without problematic fibers, German Patent Publication DE 44 45 740 A1 teaches generating an air current in the spinning chamber by opening a flap and maintaining this air current until the speed of the rotor has reached a value at which the centrifugal forces of the fibers bring about a settling of the fibers in the rotor groove which can no longer be influenced by the air current.
German Patent Publication DE 196 24 537 A1, which was filed earlier but published subsequently, teaches blowing compressed air centrally into the rotor cup in order to blow out the fibers which may disturb the spinning start process through the yarn withdrawal nozzle which is located opposite the rotor. To this end, a valve which closes the compressed air infeed is provided in the so-called hood of the spinning station, i.e., a cover covering the spinning chamber. The valve consists of a ball which is pressed against a sealing surface by a spring acting against the spinning vacuum. Under the action of the in-flowing compressed, the ball rises off of the sealing surface and the compressed air flows through the withdrawal nozzle into the rotor. If fibers and dust settle in the spring its elasticity is reduced as a consequence and a controlled air supply is no longer possible. Moreover, the spring can be blocked in such a manner that it is no longer capable of pressing the ball against the sealing surface so that false air can flow in through the valve during the spinning process.